Foamable styrene polymer compositions and method for preparing same



Chemical Company, St. Louis, Mo., a corporation of Delaware N Drawing. Filed May 16, 1958, Ser. No. 735,688 15 Claims. '-(Cl. 260-25) The present invention relates to foamable styrene polymer compositions and to methods for preparing same;

Styrene polymer foams constitute a valuable class of materials which are finding increasingly wide application in the fabrication of numerous industrial and consumer articles such as life belts, insulation partitions, ice buckets, novelties, etc. Such styrene polymer foams can be prepared by incorporating an aliphatic hydrocarbon in a thermoplastic styrene polymer and heating the resulting composition above the softening temperature of the styrene polymer. Frequently such styrene polymer foams are not as homogeneous as desired and may have rela tively largecell sizes. Foams having large cell sizes tend to be brittle and otherwise deficient in certain important physical properties. I

One method-for preparing foamable styrene polymer compositions comprises steeping styrene polymer particles, films, ribbons, etc. in an aliphatic hydrocarbon such as pentane, petroleum ethers, etc. until the styrene polymer "United States Patent 01 has absorbed the desiredquantity of hydrocarbon, e.g.,

3-10 weight percent. This process is extremely time consuming and up to days may be required to absorb thev liquid aliphatic hydrocarbon, cf., Example 5 of U.S. 2,681,321.

It is an object of this invention 'to provide foamable styrene polymer compositions which, when foamed, provide styrene polymer foams having fine cell sizes.

Another object of this invention isto provide an improved process for incorporating liquid aliphatic hydrocarbons in thermoplastic styrene polymers.

- Other objects andadvantages of this invention will be apparent from the following detailed description thereof. In accordance withv the present invention, foamable styrene polymer compositions which, when foamed, provide styrene polymer foams having fine cell sizes and improved properties are attained by intimately dispersing 10 parts of an aliphatic hydrocarbon and at least about 0.5 part of a finely divided inorganic pigment throughout 100 parts. of a thermoplastic styrene. polymer. Such foamable styrene polymer compositions can be prepared by intimately dispersing the finely divided inorganic pigment throughout the thermoplastic styrene polymer and subsequently steeping the styrene polymer .in, an aliphatic hydrocarbon.

The following examples are set forth to illustrate more a clearly the principle. and practice of this invention to; those. skilled in the art. Where parts and, quantities are men tioned, they are parts. and. quantities by weight.

EXAMPLE I I V Part A One part ofa yellow cadmium sulfide pigment having an average particle Size. of 0.31-0.45 micron is admixed with 100v parts of afinely ground polystyrene having a molecular weightof about 65,000. The externally blended mixture is extruded to obtain a uniform distribution of the pigment throughout the resin andthen ground to a particlesize of, 8-20 mesh (U.S.,Standard),.

Part B Part A is repeated employing a calcium carbonate pigment having an. average particle size; of about 0.1 micron in lieu of the cadmium sulfide pigment of Part A.

, Patented Jan. 8, 1963 I Part C 7 Part A is repeated employing an ultramarine blue pigment having an average particle size of about 5 microns in lieu of the cadmium sulfide pigment of Part A.

Part D Part F Part A is repeated employing a titanium dioxide pig ment having an average particle size of about 0.3 micron in lieu of the cadmium sulfide pigment of Part A.

Part G 1 The polystyrene employed in Part A is extruded without incorporating any pigment therein and is ground to a particle size of 8-20 mesh.

' EXAMPLE II Part A parts of the polymer from Example I,-Part A and 100 parts of n-pentane are agitated in a stirred autoclave for 7 hours at 25 C. The polymer particles are separated fromthe excess pentane and have absorbed 5% pentane.

Part B Part A above is repeated except that the time of steeping is extended to 24 hours. The polymer particles absorb 7.8% pentane.

' PartC containing the inorganic pigment absorb 5% pentane in 7 hours.

' Part D Part-C above is repeated except that the time of steeping is extended to '48 hours. The polymer particles absorb 7.7% pentane. This result should be compared with Part B above, wherein the polymer particles containing the inorganic pigment absorb 7.8% pentane in 24 hours.

Part E Each of the polymer particles from Parts A D above are foamed by placing them in boiling water for three minutes. The densities of the foamed polymers are set forth in Table I. i

TABLE I Densit Percent of Foamed Polymer Identification Foaming Resi Agent; lbs/it l In comparing the foamed resin produced from the composition of Part A with the foamed resin produced from the composition of Part C, it will be noted that, although both compositions contain substantially the same quantity of foaming agent, the resin containing the inorganic pigment has a materially lower density. A similar result is observed in comparing the foamed resins prepared from the compositions of Part B and Part D. In addition, the foamed resins containing the inorganic pigment have materially smaller cell sizes.

EXAMPLE III The polymer particles from Example I, Parts B-F are steeped in n-pentane for 24 hours at 25 C. The resulting foamable polymer particles are foamed by the method described by Example II, Part E. In each case, the foamed resin particles have fine cell sizes and a density of less than 4 lbs./ft.

EXAMPLE IV Styrene polymer particles of 8-20 mesh (US. Standard) and containing, respectively 1% of the yellow cadmium sulfide pigment described in Example I, Part A and the diatomaceous earth described in Example I, Part D are steeped in n-pentane for 24 hours at 25 C. Control styrene polymer particles containing no inorganic pigment are steeped in n-pentane for 48 hours to absorb an equivalent quantity of foaming agent. The foamable polymer compositions are then stored in sealed glass jars for 6 months. Each of the foamable polymer compositions is placed in a perforated steel mold in a quantity suflicient to occupy 8% of the mold volume. Thereafter, the resins are heated for 3 minutes with steam to prepare a-molded block of foamed polystyrene.

The foam prepared from the control foamable styrene polymer particles containing no inorganic pigment has a relatively coarse structure with the individual cells having an average diameter of 0.05-0.08". The foams prepared from the foamable styrene polymer particles containing the cadmium sulfide pigment and the diatomaceous earth have a fine structure and an average cell size of 0.0060.013. Flexural strength and modulus of elasticity values as determined by ASTM procedure D790-49T are set forth in Table II.

Polystyrene of 65,000 molecular weight and containing 1% of the silica pigment described in Example I, Part E is extruded into a sheet about 0.005" thick. The resulting sheet is steeped in n-pentane for a period of time sufficient to absorb pentane. When placed in boiling water for one minute, the sheet expands to a thickness of about 0.05". The foamed sheet has a density of about 2 lbs./ft. and a fine cell structure in which a majority of the cells have a diameter of about 0.01".

Parts B-F Part A above is repeated except that the silica pigment is replaced with, respectively, the yellow cadmium sulfide pigment, the calcium carbonate pigment, the ultramarine blue pigment, the titanium dioxide pigment and the finely ground diatomaceous earth described in Example I. In each case comparable results are obtained.

4 Part G Part A above is repeated except that no inorganic pigment is included in the polystyrene sheet. The resulting foamed sheet has a density in excess of 3.0 1bs./ft. and large cell sizes in which the diameter of the majority of the cells exceeds 0.03".

EXAMPLE VI A sheet of polystyrene of 65,00 molecular weight measuring 8" wide and 0.15" thick and having intimately dispersed therein 7% n-pentane and 1% of the silica pigment described in Example I, Part E is fed continuously through a steam chest 6 ft. long at a rate of 10 ft./minute. The sheet obtained has a fine cell size with a majority of the cells having a diameter of about 0.01 inch, a density of 2 lbs./ft. and measures 28" wide and 0.75 thick.

The function of the inorganic pigment incorporated in the styrene polymer compositions of the invention appears to be essentially mechanical in nature rather than chemical. As a result, essentially any inorganic pigment may be employed in the invention provided that it is finely divided. In general, the inorganic pigment employed should have a particle size of not substantially greater than about 5 microns and especially good results are obtained when the inorganic pigment has an average particle size of one micron or less. It is also possible to employ inorganic pigments having larger particle sizes, e.g., up to 1020 microns or even larger, although the benefits attained by the use of such pigments is not as great as those attained with smaller particle size pigments.

The term pigment is employed in the sense used in the rubber and plastic art to denote any inorganic compound or mixtures of inorganic compounds which are incorporated in a plastic material. The term is not restricted to inorganic compounds having tinctorial properties. Typical examples of the inorganic pigments that may be employed include carbon blacks, natural and heated clays, finely ground natural pigments such as limestone, bauxite, etc., multifarious inorganic colorants such as ultramarine blue, cadmium yellow, the ferrocyanide pigments, etc., the various commercially available water-insoluble inorganic salts such as calcium carbonate, calcium silicate, calcium sulfate, barium sulfate, etc., metallic oxides such as iron oxide, alumina, thoria, etc. Another very suitable inorganic pigment is diatomaceous earth, although by reason of its complex network type structure it is dillicult if not impossible to ascribe a particular particle size to this pigment. The results attained with finely divided silica pigments prepared by precipitation from water-glass solutions are outstanding and the use of such pigments constitutes an especially preferred embodiment of the invention. Such silica pigments can be prepared by the method described in US. 2,692,869.

The inorganic pigments included in the compositions of the invention, depending upon their method of manufacture, may have water chemically or physically associated therewith. Such water has no deleterious effect upon the compositions of the invention and consequently there is no need to dry the pigments.

Only a small quantity of the finely divided inorganic pigment needs to be incorporated in the styrene polymer to attain the results which characterize the compositions of the present invention. A noticeable acceleration in the rate of absorption of aliphatic hydrocarbon in the steeping process and a reduction in the cell size of the styrene polymer foams is observed when as little as 0.5 part of the inorganic pigment is dispersed throughout parts of the styrene polymer. The incorporation of more than about 8 parts of the inorganic pigment in 100 parts of the styrene polymer has little or no further effect in accelerating the rate of aliphatic hydrocarbon absorption or reducing the cell size of the resulting foamed resin. In some cases, however, larger quantities of the inorganic pigment may be incorporated in the styrene polymer for containing the inor an' other purposes such as to reduce cost, to modify physical properties, to provide more intense colors, etc.

The inorganic pigment may be incorporated in and dispersed throughout the styrene polymer by conventional mixing methods or, if desired, in some cases inorganic, pigments may be incorporated in the styrene dominant preparation of styrene, i.e., greater than 50 weight percent and preferably greater than 75 weight percent styrene. Examples of alpha,beta-ethyleuically unsaturated monomers that may be interpolymerized with the styrene include the conjugated 1,3-die'nes, e.g., butadiene, isop'rene, etc.) alpha,beta-ethylenically unsaturated carboxylic acids and derivatives thereof, e.g., acrylic acid, methyl acrylate, ethyl acrylate, Z-ethylheityI acrylate, the corresponding esters or methacrylic acid, acrylamide, methacrylamide, aerylonnriue, methacrylonitrile, monoand diesters of m'aleic a'ndj 'fumaric acid, 'etcf; vinyl esters of monobasic carboXylic acids, e.g., vinyl formate, vinyl acetate, vin l stearate, etc.'; olefins, e.g., ethylene, acenaphthylene, etc; halogenated olefins, e.g., vinyl chloride, 'vinylidene chloride, etc.; vinyl ethers, e.g.,'vinyl methyl ether, vinyl butyl ether, etc. If desir'ed, blends of a major am0unt,'e.g., greater than 50 weight percent, of a styrene polymer with minor amounts, 'e.g., less than 50 weight percent, of other polymers may be employed, e.g., blends of a styrene polymer with a rubbery diene polymer, or the analogous compositions 'ob- 'tained by polymerizing styrene monomer inthe presence of a rubbery diene polymer. In'an'y of the above type 1 resins, all or a portion of the styrene may be replaced with its closely related homologues such .as alpha-alkyl substituted monovinylidene aromatic hydrocarbons, e.g., alpha-methylstyrene, alpha-ethylstyr'ene, em; rin'g-alkyl sl'ibstitutedv monovinyl-idene aromatic hydrocarbons, e.g.,

'o-, mand p-yinyl-toluene, o-, mand p-ethy1styrene, alpha-methyl-2,4 dimethylstyrene, 2,4-dimethylstyrene,

'etc.; ring-halogenated monovinyliden'e aromatic hydrocarbons, 'e.g., o-, m "and p-chlorostyrene, 2-,4 dichlor'ostyrene, etc.; ring-alkyl substituted halogenated monovin'ylidene aromatic hydrocarbons, e. 2-chloro-4- methylstyrene, etc. In "general, the styrene polymers employed should haveamolecular weight in the range of about 40,0001 00,0 0'0 as determined by the St'audinge'r method. m m e H The aliphatic hydrocarbons included in the compositions of the raven-nan boil within the range of from about 10 0. to about r00 0. and preferably within the range of from about 30 to about 80 'C. Exa'mpies ot such hydro arbons include 'p'e'ntane, is'open'ta'ne, -c'yclopenrane, hep'tane, etroleum etheis boiling within the previously described temperature ranges, etc. It is permissible, and {in some cases desirable, to admin other volatile organic liquids with the aliphatic hydrocarbon. In particular, good results frec' uently are obtained em loying jiniirtures of 70 95 weight percent of an =al hatic hydrocarbon and, correspondingly, Q-S weight percent "of a 'normally liquid lower halogenated hydrocarbon such as methylene chloride. Normally the aliphatic hydrocarbon will be "em- I 'ployed in amounts of about 340 and preferably about 5-3 parts per 100 parts ofthestyrene polymer.

The foal ble st rene polymer compositions 'p'referably are an ed by steeping ast' renepolymer having an inorganic ent homogeneously dispersed therein in an aliphatic hydrocarbon. The absolute rate or anpha'tic hydrocarbon absorption is dependent upon the surface areaper unit Wei ht possessed by the styreae polymer 1c pigment. For this rea on, the styrene polymer thatfis -to be 'st'eepe'd, whether in the form of particles, films, filaments or sheets, should have at least one dimension which is not greater than about '5 millimeters.

One method for steeping the styrene polymers consists of simply contacting the styrene polymer containing the inorganic pigment with a large excess of the aliphatic hydrocarbon and separating the polymer therefrom after it has absorbed the desired quantity of the aliphatic hydrocarbon. In another embodiment of the invention, the styrene polymer containing the inorganic pigment and the aliphatic hydrocarbon may be-dispersed in a large volume of water and heated to an elevated temperature, preferably in an autoclavef The steeping may be carried out at temperatures ranging from about 0 C. to the boiling point of the hydrocarbon or even higher if the steeping is carried out under pressure. At room temperature or above, agitation should be provided to prevent agglomeration of the styrene polymer particles or films.

The foarnable polymer compositions ofthe invention can be prepared by alternate procedures if desired. For

example, the inorganic pigment and the aliphatic hydrocarbon can be dispersed .in styrene monomer which is subsequently polymerized. In still another embodiment of the invention the inorganic pigment and the aliphatic hydrocarbon can be dispersed within the thermoplastic styrene polymer by mechanical mixing as on rubber mills or in a Banbury mixer or in screw type extruders.

I The above descriptions and particularly the examples are set forth by way of illustration only. Many other modifications and variations thereof can be made without departing from the spirit andscope of the invention herein described.

This application is a continuation-in-part of my copending application'Ser. No. 559,502, filed January 16, 1956, now abandoned.

What is claimed is:

l. A solid particulate foamable thermoplastic polymer composition consisting essentially of 100 parts of a thermoplastic styrene polymer having intimately dispersed therein about 3-10 part of an aliphatic hydrocarbon boiling within the range of'about 30-80 C. and

at least about 0.5 part of a finely divided inorganic pigment having anaverage particle size of not substantially greater than about 5 microns.

2. A composition as in claim 1 wherein the inorganic pigment is silica.

3. A composition as in claim 1 wherein the inorganic pigment is diatomaceous earth.

'4. A composition as in claim 1 wherein the inorganic pigment is calcium carbonate.

'5. A con'ip'o'sition as in claim 1 wherein the inorganic pigment is c'adium sulfide.

6. A composition as in claim 1 pigment is ultramarine blue.

7. Asolid sheet of a foamable thermoplastic polymer composition consisting essentially of 100 parts of a thermoplastic styrene polymer having intimately dispersed therein about 3-10 parts'of an aliphatic hydrocarbon boiling within the range of about 30-80 C. and at least about 0.5 part of an inorganic pigment having an average particle size of not substantially greater than about 5 microns. m H

8. The method for preparinga foamable styrene polymer composition which consists of steeping a styrene polywherein the inorganic the"; composition in analiphatic hydrocarbon boiling with- 9. The method ofcla'im 15in which 0.5-8 parts o'f'the I inorganic pigment are intimately incorporated in 100 parts of a styrene homopolymer.

10. The method of claim 9 in which the inorganic pigment incorporated in the styrene homopolymer is silica.

11. The method of claim 9 in which the inorganic pigment incorporated in the styrene homopolymer is diatomaceous earth.

12. The method of claim 9 in which the inorganic pigment incorporated in the styrene homopolymer is calcium carbonate.

13. The method of claim 9 in which the inorganic pigment incorporated in the styrene homopolymer is cadmium sulfide.

14. The method of claim 9 in which the inorganic pig- 8 ment incorporated in the styrene homopolymer is ultramarine blue.

15. The method of claim 8 in which the styrene polymer Composition is steeped in an aliphatic hydrocarbon 5 boiling within the range of about 3080 C.

References Cited in the file of this patent UNITED STATES PATENTS 10 2,577,743 De Long Dec. 11, 1951 2,744,291 Stastny et al. May 8, 1956 2,848,428 Rubens et al Aug. 19, 1958 2,941,965 Ingram June 21, 1960 

1. A SOLID PARTICULATE FOAMABLE THERMOPLASTIC POLYMER COMPOSITION CONSISTING ESSENTIALLY OF 100 PARTS OF A THERMOPLASTIC STYRENE POLYMER HAVING INTIMATELY DISPERSED THEREIN ABOUT 3-10 PARTS OF AN ALIPHATIC HYDROCARBON BOILING WITHIN THE RANGE OF ABOUT 30-80*C. AND AT LEAST ABOUT 0.5 PART OF A FINELY DIVIDED INORGANIC PIGMENT HAVING AN AVERAGE PARTICLE SIZE OF NOT SUBSTANTIALLY GREATER THAN ABOUT 5 MICRONS. 